How's it going guys? Well, the problem is I've been jipped out of a few points on my Bio exam, and I believe I was completely right. First off, one of the questions asked was "If a sponge and a brick have the same density, which has the greater volume?" I just filled in an answer and was going to argue it, but wouldn't you need to know mass as well to accomplish this? Hence D=M/V. I asked her about it and she said no, you just need to know that brick weighs more per unit, and I retorted with you just decribed density again. She then discontinued with my questioning. Another thing was that she marked off for me writing ---> = reaction, and some other kid in the class wrote ---> = yields, and she said the correct answer was chemical reaction. I'd say I'm right here, I know the other kid is 100% right. She basically marks off if it isn't her strict definition from the notes. Is this something that I should be bringing up to a higher power?

Well, -----> means reaction direction. For us, this is the case. For you I don't know, maybe she wants you to specify as a chemical reaction.

As for density, the only way for the sponge and brick to have the same density is for both their masses and volumes to be different. We know that their masses aren't equal, so in order for us to have similar densities the only way is to have differing volumes. You must then rationalize to say that the sponge must have the greater volume in this case because it is porous.

I see what you're saying. Well my major's chemistry, and I try and stay strict to the math, maybe that's why I didn't even bother to think about the question. The way I saw it was A and B have the same density, yada yada. I guess it's all heresay on what's right. But for her to completely shun my idea and tell me that I wasn't even partially right is ridiculous.

Yes she is rather impractical. I just don't know whether to confront her again about it or let it go. I explained it logically to her, and the equation isn't lying to her, but she still just won't have it. If the sponge and brick had a density of 2g/cm3, one could weigh 200 grams and the other could weigh 100 grams, and I would have no idea. I hate arguing with superiors, it's almost always lose-lose.

And to answer your "maybe she meant they weigh the same" comment, I answered they have the same volume and got it wrong.

You will quickly learn that Professors are human and make mistakes. And many professors are too arrogant to admit it. In my experience most college professors tend to think of their students (especially lower level students) as a distraction from their real job.

The important thing is you learn if you are really wrong or he/she is right and you learn the material.

If we are talking 5% off one assignment or test which is only 20% of your final grade, that is only 1% of your total grade. That 1 % is nothing.

Having the teacher like you is more important then that 1%, if you have a 89% and they hate you, you might still get a B. If you have an 89% and you have impressed them more then likely you will get the A.

It is sad, but that is how it is. Just do not let it interfere with your actual education.

If a sponge and a brick have the same density, which has the greater volume?

If their densities are the same then their volumes must be the same (for the same mass), which is correct if you don't make any assumptions about bricks or sponges. If one has a different volume then they must have different masses also, which defeats the point of the question. (Which is heavier a tonne of bricks or a tonne of sponges?)

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Another thing was that she marked off for me writing ---> = reaction, and some other kid in the class wrote ---> = yields, and she said the correct answer was chemical reaction. I'd say I'm right here, I know the other kid is 100% right. She basically marks off if it isn't her strict definition from the notes.

---> is an arrow. It doesn't mean anything out of context. If you have been given notes on what ---> means then that is the correct answer, whatever the teacher wrote in the notes. So I think you are wrong on this one, this time, sorry.

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As for density, the only way for the sponge and brick to have the same density is for both their masses and volumes to be different.

Not technically correct. They could both have the same mass and volume. They should both have the same ratio of mass to volume, i.e. density LOL

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We know that their masses aren't equal,

No we don't, do we?

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You must then rationalize to say that the sponge must have the greater volume in this case because it is porous

It is a little ambiguous if you need to make such assumptions.

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Assuming that's the exact wording of the question, there is not enough data to answer.

Perhaps she meant "if they weight the same" - but it is not given in the question, so it is not part of the question.

I agree with Borek.

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I mean, the sponge could literally be much larger than the brick and have a greater mass and weigh more than the brick.

This wouldn't change the density part of the question though.

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I answered they have the same volume and got it wrong.

So what is the teachers answer then?

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In my experience most college professors tend to think of their students (especially lower level students) as a distraction from their real job.

Well one undergraduate student with one 5 minutes question may seem to be not much hassle, but what about the other 200/400/600 students? Lets say you had 300 first year students and each one only wanted , say 3 minutes of your time, that is 15 hours of contact!! Not to mention other students, staff, research, eating sleeping, life LOL, cut your teachers some slack!!

Well in that case if the brick is the answer the teacher should have made some statement about the mass of the brick compared to the sponge. Your teacher is wrong, you are right, however this doesn't mean you'll get extra marks, sorry

I'd just like to say that mike seriously kicked butt with that post. Everyone else in the post did great, so don't think I'm putting everyone else down. But the sheer size of mike's post is impressive +snack!

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Well one undergraduate student with one 5 minutes question may seem to be not much hassle, but what about the other 200/400/600 students? Lets say you had 300 first year students and each one only wanted , say 3 minutes of your time, that is 15 hours of contact!! Not to mention other students, staff, research, eating sleeping, life LOL, cut your teachers some slack!!

"If a sponge and a brick have the same density, which has the greater volume?"

As has been said already - if there is no other information available then it is impossible to tell. For equal mass they have equal volume BECAUSE they have equal densities. Are you sure your teacher is a Proffessor? How old is she? She is clearly wrong!

Why not? Since she can't answer the brick question properly, her authority to define "--->" is definitely questionable.

Logged

"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006